Manufacturing processes of semiconductor devices include a process of polishing a dielectric film, e.g., SiO2, and a process of polishing a metal film, e.g., copper or tungsten. Manufacturing processes of backside illumination CMOS sensor and through-silicon via (TSV) include a process of polishing a silicon layer (silicon wafer), in addition to the polishing processes of the dielectric film and the metal film. Polishing of a wafer is terminated when a thickness of a film (e.g., the dielectric film, the metal film, or the silicon layer), constituting a wafer surface, has reached a predetermined target value.
Polishing of a wafer is carried out using a polishing apparatus. In order to measure a film thickness of a non-metal film, such as a dielectric film or a silicon layer, the polishing apparatus generally includes an optical film-thickness measuring device. This optical film-thickness measuring device is configured to direct a light, which is emitted from a light source, to a surface of the wafer, to measure intensity of reflected light from the wafer with a spectrometer, and to analyze a spectrum of the reflected light to thereby measure the film thickness of the wafer.
In the optical film-thickness measuring device, a quantity of light emitted by the light source influences measuring of the film-thickness of the wafer. For example, if quantities of light, directed to a plurality of measurement points on the wafer, are different from each other, the accuracy of the film-thickness measurement changes due to a difference in optical conditions. As a result, even if the film thickness of the wafer is the same, a measured value of the film thickness can vary. Furthermore, if the quantity of reflected light from the wafer is too large relative to an effective measuring range of the spectrometer, measuring of an accurate film thickness is hindered.